The benefits of thermally modified wood

Here at EcoChoice, whilst we’re keen to embrace timber at its most natural and sustainable, we’re also passionate about the use of timber technology to increase its appeal or performance.

Things don’t get more cutting edge than Thermowood. Thermowood, also known as thermally modified wood, is growing in popularity throughout the UK and the rest of the world. Here, we deliver the ultimate guide to Thermowood, so you can discover what all the fuss is about.

What exactly is Thermowood?

As the name suggests thermally modified hardwood or softwood have been heat treated to unlock some pretty impressive benefits. The wood is treated using a completely natural and non-toxic practice, where it is baked to a temperature of more than 100 degrees.

The heating process takes place in an environment that’s devoid of oxygen, removing organic compounds from the timber cells to modify the timber permanently.

The resulting timber product is a lot more stable, with minimal moisture absorption. Durability is also enhanced, leaving the insects and fungi known to cause timber damage with little to feed on. With less water content,Thermowood is particularly lightweight, making it suitable for a vast range of applications.

In addition to the wood’s internal structure altering as a result of intense heat treatment, Thermowood looks different. Thermally-modified wood generally sports a rich, dark brown appearance – providing an attractive, and almost exotic look.

This chocolate colour can be maintained with the right finishing or can be left to weather naturally to a grey shade, a favourite of many architects and developers.

Several tree species are suitable for thermal modification, including Ash, Spruce, Pine, Frake, and Ayous. Oak is not widely available Thermodified since it is already naturally durable, but many are utilising thermal modification practices to enhance its appearance.

Different types of thermally modified wood

There isn’t just one type of thermodified wood – there are a number of different ways to thermally modify wood, which involve using different technologies. The key types are:

Plato Process
The Plato Process is a two-step thermo modification process that originates from The Netherlands. It involves subjecting the wood (which has been saturated with water) to hydrothermal treatment at high pressure at temperatures between 160°c and 190°c. The moisture content of the wood is then reduced to 10% and the wood is then dry cured under pressure at temperatures between 170°c and 190°c. The whole process can take up to 7 days.

Oil Heat Treatment
Oil Heat Treatment (OHT-Process) is a one step process that originates from Germany and sees the wood heated in a bath of oil at temperatures of between 180°c and 220°c.

Retification
Originating in France, Retification is a one step process that sees wood which has less than 12% moisture content placed in a high nitrogen atmosphere with less than 2% oxygen content. The product is known as Retiwood or New Option Wood

Les Bois Perdure
Also originating in France as the name suggests, this is a one step process that sees freshly cut and dried timber heated using steam, which is created by using the leftover moisture in the wood.

ThermoWood
ThermoWood^® is a registered process that originates from Finland. It is also known as Premium Wood. Like the Les Bois Perdue process, it involves using steam and pressure, but it can also be used to treat green wood (i.e. recently cut wood that has not been dried to allow for the evaporation of internal moisture). The process takes up to 72 hours.

Why should you choose thermally modified wood?

Thermodified wood unlocks numerous advantages with its lightweight and dimensional stability being just two of the factors that make thermally modified wood the first choice across many projects.

Thanks to its durability and minimal moisture content, it doesn’t warp or lose shape as much as natural timber. It instead retains its shape for many years to ensure optimum performance with very little maintenance. Its resistance to mould, decay and insects is another plus-point.

Thermowood isn’t just great for the projects it’s used on, it’s great for the environment too as GardenSite details:

“Due to the way Thermowood® is treated using only heat and water vapour, rather than chemicals used normally, it allows the process to be much more environmentally friendly. Which is why the majority of people choose this process, along with its strength and durability.”

The chemical-free process used to modify the wood is beneficial to health when compared with other chemical alternatives. Even coming into contact with chemically-treated timber or breathing in the air that surrounds it can be harmful to human health. Thermowood is therefore a healthy and safe alternative to the commonly found pressure treated timber.

Where can Thermowood be used?

Thanks to its strength and mould resistance, and excellent thermal qualities, Thermowood is a natural choice for cladding. It can also be successfully used in other outdoor applications, including those subject to continuous wet conditions such as timber decking, siding, and flooring. It is even providing enviable solutions in less stable, high-moisture environments, like basements.

Unlike pressure treated wood products, Thermowood can be used in conjunction with metal. Its low moisture content means metals coming into contact with thermally modified wood don’t corrode as much – although stainless steel is always recommended.

What Are Preservative Finishes on Thermowood?

Preservative treatments are applied to timber to protect against fungal decay, insect attack and rot. Rather than altering the timber’s cellular structure, they effectively create a barrier around the wood which enhances its durability for a longer-lasting timber product.

When carried out before installation, these preservatives can be impregnated deep into the timber for long-lasting protection which goes far beyond the surface. This is super handy if you plan on cutting the timber, ensuring that every new surface you create has the same level of durability.

ThermoWood vs. Preservatives

When it comes to choosing between ThermoWood and preservatives, there is a lot to consider. We have put together this handy chart to make weighing up your options a whole lot easier:

When to Use ThermoWood or Preservatives

Thermo modification and preservative treatments can both be great options, depending on the application of your timber.

In general, we recommend ThermoWood for exterior applications which you do not want to be constantly maintaining, such as external decking and cladding applications where ground contact is avoided and correct detailing is used. As a result of its enhanced structural integrity, it also makes a great option for interior joinery.

Preservative treatments are commonly used in both domestic and commercial projects, particularly where ground contact or high moisture exposure is expected, such as garden decking, fences and outdoor furniture. Just make sure to choose an eco-friendly finish for sustainable construction.

How can I choose the highest quality Thermowood?

You can find the highest quality thermally modified timber products right here. Ecochoice are pioneers in the Thermowood market. We were in the first to supply FSC® certified hardwoods outside the standard thermally modified Spruce and Pine.

Find out more about our new Thermowood species by contacting our team direct on 0345 638 1340 or emailing info@ecochoice.co.uk.

Image: Yamoka / Shutterstock.com